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Feb. 7, 2011 -- Three-year-olds who eat diets rich in fat- and sugar-laden processed foods may have slightly lower IQ scores at age 8 than their peers with healthier eating habits, a new study shows.

The small, but measurable, difference in IQ scores detected in the study between kids who ate the most processed foods at age 3 and kids who ate the least suggests that optimizing a young child’s diet may do more than help prevent obesity; it may also give kids a lasting brain boost.

Nutrition and IQ

Researchers followed nearly 4,000 children in Southwest England from birth through age 8. They asked their parents to fill out detailed questionnaires about their youngsters’ diets at ages 3, 4, 7, and 8 1/2.

Ready-to-eat foods high in fat and sugar were considered to be processed.

After adjusting for other things that may influence intelligence testing, like age, sex, and family income, researchers found that kids who ate diets high in processed foods at age 3 had slightly lower IQ scores by age 8 1/2.

The study also showed children who at age 3 ate what the researchers termed a “healthy diet” high in salad, fruit, vegetables, rice, and pasta had an associated higher IQ at age 8 and a half.

Dietary patterns between the ages of 4 and 7 appeared to have no impact on IQ.

The study was published online in the Journal of Epidemiology and Community Health.

Previous studies have suggested that early childhood nutrition may play a role in intelligence and brain development.

“We know already that breastfeeding has quite an effect on IQ, so it makes sense that there’s something going on with diet,” says study researcher Kate Northstone, from the School of Social and Community Medicine at the University of Bristol in the U.K. “I was surprised that we found this effect at 3 rather than 8. That for me is the interesting point. It was the 3-year-olds and what they ate, rather than, say, at 4, 7, and 8.”

Child IQ: Other Factors Matter

But other researchers remain unconvinced.

"The results suggest, at most, a weak relationship between characteristics of the child diet, as reported by the parent and a measure of IQ at age 8,” says Aryeh D. Stein, PhD, MPH, an associate professor at the Rollins School of Public Health at Emory University in Atlanta.

Stein has studied the impact of nutrition on children but was not involved in this study.

“Other studies, especially in the context of undernourished populations such as Guatemala in the 1970s, have shown that food supplementation prior to age 3 improves cognition, but there is little evidence for any substantial impact of children’s diets in Western populations,” Stein says.

“One important consideration is that social factors such as parental socioeconomic position, schooling, etc., are likely to influence both the child’s diet and the child’s performance on IQ tests, and hence the causal interpretation of observational studies such as this one remains challenging.”

Processed Food: Striking a Balance

Northstone says she understand the pressures busy parents face, and that the important thing isn’t to make sure these foods never touch a child’s lips, only that they don’t replace fruits and vegetables.

“I have a 6-year-old boy,” Northstone says, “and I know how hard it is to say ‘no’ to the crisps and ‘no’ to the sweets and ‘no’ to the chips. You don’t have to always say ‘no.’ Just make sure they also get some fresh food, some fresh fruit, fresh veg. And every now and then, say ‘no’ to the chocolate.”